1. Field of the Invention
The field of this invention is within the impact printer field and in particular, the line printer field directed toward using a line printer having multiple hammers with tips that strike a ribbon that impacts an underlying print media such as paper. The line printers are such where they have a number of hammers on the hammerbank which are held by a permanent magnetic force and then released by electromagnetism. When released, the hammer tips strike a ribbon which impacts the underlying media to be printed upon. During the striking of the ribbon, the ink is depleted from the ribbon in a manner whereby variances of appearance of the printed product can be apparent.
2. Prior Art
The prior art with regard to line printers incorporates various line printers having singular rows of hammers with printing tips in a hammerbank. These rows of hammers in a hammerbank are released from permanent magnetic retention by an electromagnetic coil. The hammer tips when released proceed toward an inked ribbon for impacting against a media to be printed upon.
Recently, a new hammer orientation has been developed wherein a hammerbank having dual hammers incorporates an upper and lower set of hammers. These upper and lower sets of hammers are released so that the ink or print ribbon is impacted by two hammers in an upper and lower or duplex banked mode. This dual print activity by the hammers puts a double load on the capacity of the ink or print ribbon for providing ink. To this extent, the capacity of the ink ribbon if it is consistent through the ribbon causes variances because of variously differently oriented strike zones.
The term banding is a term wherein one of two printed lines will be darker on the right side than on the left. The next line will be darker on the left and lighter on the right.
The two rows of hammers which are on top of each other having an upper and lower set of hammers are spaced approximately one sixth of an inch apart. They simultaneously print adjacent rows, effectively doubling the through put of the printer.
The printing is by a printed dot when the hammer strikes against an inked ribbon leaving a dot on the paper or underlying media. A one inch or wider inked ribbon reciprocates or translates continuously between the hammers and the paper or media at an incline. This incline is to allow for greater ribbon use since the incline causes the ribbon to cross the total number of hammers. The incline helps to eliminate a concentration of the hammers impacting the print ribbon in one particular area such as down the middle.
A heretofore unsolved problem with the dual row arrangement of hammers is that the center area across the ribbon width of the ribbon is generally struck twice or at least more than once during each pass of the ribbon. To the contrary, the outer boundaries are only struck once or less. The result is that after a relatively small number of printed pages a light and dark pattern of printed lines appears.
For instance, one of the two printed lines such as that printed by the upper row of hammers will be darker on the right side than on the left. The next line of print as printed by the lower row, will be darker on the left and lighter on the right side. This particular phenomena or effect is known as banding.
A second lesser disadvantageous effect occurs which is addressed by this invention. This second effect is that the printing density varies from darker appearances at the edges of the page, to lighter appearance toward the middle of the page. This is due to the high ink concentration of the unused edges of the ribbon. These boundaries are necessary to insure that in all cases the end hammers always strike inked ribbon. Since the ink in these boundary areas does not get removed from the ribbon as the result of hammer strikes it tends to defuse into the adjacent area. This particular characteristic is referred to as a diffusion effect. The diffusion effect causes the print at the edges as previously stated on the paper to be darker than the center. This is independent of the banding effect.
The diffusion effect can be worse on the left side of the paper than on the right side. This is due to the effect of gravity on the ink in the ribbon. The reason is that the left side of the printed page derives its ink from the lower left portion of the inclined ribbon.
The invention hereof tends to overcome the foregoing deficiencies of the prior art by providing for an ink or print ribbon which has a variable characteristic. When being struck, it compensates for the fact in certain portions the ribbon is being struck twice as much or more than the other portions. These particular portions are generally in the central area where the larger amount of strikes take place.
In summation, the invention reduces banding, diffusion, and gravity effects by locating inks with different printing yields provided by varying concentrations, pigment contents, or viscosity on different portions of the ribbon such as in the longitudinal central portion and the edge portions in such a manner as having a greater printing yield in the middle and a lesser printing yield on the edge portions.
More specifically, the highest ink concentration or print yield is located in the middle of the ribbon or the longitudinal center. This generally corresponds with a double or more than one strike zone. Proportionally ink having a lesser yield is located at the upper and lower boundary areas which are used less. These longitudinal boundary areas are such where the lower ink yield provides for the lesser hammer strikes which can be in a range of one half the hammer strikes as received in the longitudinal center of the ribbon. In this manner, the ribbon will be located with appropriate ink yields on different portions based upon consumption, thereby reducing the banding, diffusion, and gravity effects.
It has been found that this is extremely helpful with regard to impact printers and particularly to double row line printers where hammers are queued or banked above each other. The net result is an. improved printout which can be seen hereinafter in the specification hereof.